A volcano can be described as an opening, or rupture, in a planet’s crust, that allows hot ash, magma, and gases to evolve from underneath the surface. The term ‘volcano’ is a derivative of Vulcano, an island off Sicily that had been named after Vulcan, the Roman god of fire.

Normally volcanoes are present where tectonic plates are converging or diverging. A mid-oceanic ridge, such as the Mid-Atlantic Ridge, contains volcanoes resulting from divergent tectonic plates getting apart; the Pacific Ring of Fire has a number of volcanoes formed by convergent tectonic plates coming intact.

On the other hand, volcanoes do not develop at their own at points where two tectonic plates run across each other. Volcanoes can develop under zones of the Earth’s crust having thin or weak lining (surface) known as “non-hotspot intraplate volcanism”, such as in the Wells Gray-Clearwater volcanic field, the African Rift Valley, and the Rio Grande Rift in North America and the European Rhine Graben having Eifel volcanoes.

Mantle Plumes also form volcanoes. These so-called hotspots, can be present quite off the plate boundaries, such as for example at Hawaii. Elsewhere in the solar system hotspot volcanoes can be traced on rocky planets and moons.

Many historical works associate volcanic outpourings to supernatural dimensions, such as the wills of gods or deities. According to pagan Greeks, volcanoes’ immeasurable power would be attributed with the acts of different deities; not only this, even 17th century German astronomer Johannes Kepler also went to the extent of saying that they (volcanoes) were route to channel out outpourings of the Earth’s tears.

An expert, Jesuit Athanasius Kircher, has proposed a quite different idea in the seventeen century. He had been observing a series of eruptions of Mt. Etna and Strombli. Afterwards he came to visit the crater of Vesuvius and published his study picturing an earth with a great fire in the core that is extended to numerous channels carrying loads of burning sulfur, bitumen and coal across the crust in the form of volcanic eruptions.

To explain volcanic behavior, a number of theories were propounded before the modern interpretations of the composition of the Earth’s mantle — a semisolid material as of studied now.

Decades after the nature of earth’s mantle was understood, that radioactive materials and compression could be the source of heat, their roles in eruption were particularly neglected. The phenomenon of volcanic eruption was described to have been primarily interlinked with two factors: chemical reactions and thin layer of molten rock just below the crust.

Deep inside the earth the rock melts because of extremely high temperature. This molten rock, called magma, is lighter than the surrounding rock. This can be understood with the help of the example of an object floating on water because of having less density than water. Same principle acts here — the relatively low density of magma causes it to pop out of the earth’s crust where there is thin zone of crust available.

If there are water and dissolved gases in magma, upon reaching the surface, water and dissolved gases will burst into steam and gas, causing a violent explosion. The phenomenon can be attributed with the process of shaking a tin pack of coke and then suddenly popping its tab.